Apparatus for controlling the tension in a web



May 30, 1967 E- EBERLIN 3,322,315

APPARATUS FOR CONTROLLING THE TENSION IN A WEB Original Filed Aug. 22, 1963 FIG.

En /m AINTHONY EB RLW United States Patent Ofilice 3522,13 Patented May 30, 1967 3,322,315 APPARATUS FOR CONTROLLING THE TENSION IN A WEB Edgar Anthony Eberlin, Birmingham, England, assignor to James Halley & Sons, Limited, West liromwich, England, a British company Continuation of application Ser. No. 303,816, Aug. 22, 1963. 'this application June 2, 1966, Ser. No. 554,912 Claims priority, application Great Britain, Sept. 6, 1962, 34,130/ 62 8 Claims. (Cl. 226-44) This application is a continuation of application Ser. No. 303,816 filed Aug. 22, 1963, now abandoned.

The invention relates to apparatus for controlling the tension in a web, for example of paper, plastic, foil, cloth or the like, during its transit through processing machinery, the apparatus being of the kind employing a roller commonly called a loop or dancing roller, which is mounted to carry a loop in the web and is movable, usually vertically, at right angles to its axis of rotation to lengthen or shorten the loop of the web in response to a decrease or increase in the tension of the web respectively from a mean position established by a predetermined thrust imparted to the roller in accordance with the required tension, the movement of the roller from its mean position being sensed and employed to control a feeding or take up mechanism so as to decrease or increase respectively the rate of feed of the web and so correct the departure of the web from the required tension.

The present invention has for its object a web tensioning apparatus of particularly simple and reliable construction which is able to exercise a fine and accurate tension control.

The present invention consists of an apparatus for controlling tension in a web comprising a loop roller supported by fluid operated pistons and cylinders with the latter connected to a source of substantially constant fluid pressure.

Preferably said cylinders are connected to a common fluid reservoir of relatively large capacity, and a fluid pressure input to said reservoir is fed through a pressure regulator which can be adjusted to vary the pressure in said reservoir and hence the tension applied by the loop roller to the web.

One example of the practical realisation of the invention is illustrated in the accompanying drawings, wherein:

FIGURE 1 shows schematically a web tensioning system according to the invention; and

FIGURE 2 is a longitudinal cross-section of a piston and cylinder of the type employed in the system of FIG- URE 1.

In the embodiment of the invention illustrated in FIG- URE 1 the web 2 passes through the nip between a pair of feed rollers 3 and 4 driven from an electric motor 5, and thence passes beneath a horizontally spaced apart parallel pair of horizontally extending idle rollers 6 and 7. Mounted for movement in a vertical plane between and parallel to the axis of the idle rollers 6 and 7 is a loop or dancing roller 8 rotatably mounted on a shaft 9 which is supported in the vicinity of its two ends by a pair of single acting fluid-operated pistons and cylinders 10 and 11 disposed one on each side of the web and beneath the shaft 9.

Both of the cylinders 10 and 11 are fed from a common reservoir 12 or accumulator of large capacity compared with that of the cylinders 10 and 11 so that movement of the pistons results in an insignificant change in pressure in the reservoir 12. The reservoir 12 is in turn fed from a fluid source (not shown) through an adjustable pressure regulator 13 which can be controlled to vary the pressure in the reservoir and thus the thrust applied by the pistons 10 and 11.

The loop roller shaft 9 is engaged in the forked end of an arm 14 fast on a spindle 15 driving an error signal generator 16 in a conventional type of servo system 17 designed to control the speed of the drive imparted to the feed rolls 3 and 4 by the electric motor 5.

In operation, the pressure regulator 13 is set to a given value to maintain a selected substantially constant pressure in the reservoir 12 whereby a required upward thrust is imparted to the two ends of the loop roller shaft 9 carrying a loop of web 2 between the two idle rollers 6 and 7 so as to create the required tension in the web. Following any increase or decrease in tension in the web 2 the length of the loop in the web decreases or increases respectively thereby depressing or elevating the loop roller '8 which still maintains its selected thrust on the web, and this loop roller movement transmits via shaft 9, forked arm 14 and spindle 15, an equivalent angular movement to the error signal generator 16 so as to increase or decrease the speed of the drive imparted to the feed rollers 3 and 4 thereby to correct the web tension.

It will be appreciated that for sensitive control of the web tension the friction between the pistons and cylinders 10 and 11 must be of a low order. To this end, and as shown in FIGURE 2, each piston 20 is of substantially smaller diameter than that of the bore of its cylinder 21 and a seal between these parts is made by a rubber bag like diaphragm 22, having an upper closed end which supports the piston 20 with a fold '22 in the diaphragm between the periphery of the piston and the cylinder so that movement of the piston in the cylinder is accompanied by rolling of the fold in the diaphragm along the internal wall of the cylinder. By this means direct frictional engagement of the piston with the cylinder is avoided and the friction present is only that resisting flexing of the diaphragm 22.

Preferably the fluid pressure medium employed is air rather than a liquid to provide resilience in the mounting of the loop roller 9.

I claim:

1. A web tensioning apparatus comprising a pair of web feed rollers, an electric motor driving said rollers, a pair of parallel idle rollers having fixed axes, a rotatable loop roller mounted on a shaft for vertical movement between and parallel to said idle rollers, a pair of piston and cylinder units supporting opposite ends of said shaft, a large capacity reservoir connected to supply constant fluid pressure to both of said cylinders, the relative capacities of said reservoir and said cylinder units being such that changes in position of the loop roller with changes in size of the loop during changes in rate of feed of said web do not significantly change said fluid pressure, an adjustable pressure regulating valve for maintaining a desired fluid pressure in said reservoir, an angularly displaceable element operably connected to be responsive to the vertical movement of said shaft caused by a variation in size of said loop due to variation in the rate of feed of said web, an error signal generator driven by said element in proportion to said shaft movement, and a servo system under the control of said generator for compensatively varying the speed of drive between said motor and feed rollers to maintain said desired web tensron.

2. Apparatus for controlling the tension in a web that is being transported by feed means having a drive motor, said apparatus comprising a pair of spaced parallel web engaging idler rollers arranged on fixed axes, a web engaging loop roller disposed in a loop of said web formed between said idler rollers, fluid pressure means comprising a pair of cylinder and piston assemblies supporting said loop roller at opposite sides of the web, said cylinder and piston assemblies constituting the sole support for said loop roller, and means for supplying a selected constant fluid pressure to both of said cylinders whereby to cause said loop roller to exert and maintain suflicient thrust on the web in said loop to produce a desired tension in the moving web regardless of changes in position of the loop roller caused by changes in the rate of feed of the web that result in changes in size of the loop, each of said cylinder and piston assemblies comprising a foldable flexible diaphragm within the cylinder containing said pressure and a piston supported within a circumferential fold in said diaphragm.

3. Apparatus for controlling the tension in a web that is 'being transported by feed means having a drive motor, said apparatus comprising a pair of spaced parallel web engaging idler rollers arranged on fixed axes, a web engaging loop roller disposed in a loop of said web formed between said idler rollers, fluid pressure means comprising a pair of cylinder and piston assemblies supporting said loop roller at opposite sides of the web, and means for supplying a selected constant fluid pressure to both of said cylinders whereby to cause said loop roller to exert and maintain suflicient thrust on the web in said loop to produce a desired tension in the moving web regardless of changes in position of the loop roller caused by changes in the rate of feed of the web that result in changes in size of the loop comprising a common fluid pressure reservoir having a large capacity compared with said cylinders and being constantly connected by conduit means into both of said cylinders, the relative capacity of said reservoir and cylinders being such that normal erational movement of said pistons resulting from said changes in position of said loop roller with changes in the rate of feed of said web produces only insignificant changes in pressure in said reservoir.

4. In the apparatus defined in claim 3, means defining an inlet for supplying fluid under pressure into said reservoir and a variable fluid pressure regulator in said inlet for maintaining a desired fluid pressure in said reservoir.

5. In the apparatus defined in claim 3, said cylinder and piston assemblies constituting the sole support for said loop roller.

6. Apparatus for maintaining constant tension in a web that is being transported by feed means having a variable speed drive motor, said apparatus comprising a pair of spaced parallel web engaging idler rollers arranged 0n fixed axes, a web engaging loop roller disposed in a loop of said web formed between said idler rollers, fluid pressure means supporting opposite ends of said loop roller and comprising a pair of cylinder and piston assemblies and means for supplying a constant fluid pressure to both of said cylinders whereby to cause said loop roller to exert and maintain sufficient thrust to produce a desired tension in the moving web regardless of changes in position of the loop roller caused by change in the rate of feed of the web that result in changes in size of the loop, said loop roller being displaced by the web when said loop changes in size in response to changes in the rate of feed of said web, and means responsive to said displacement of said loop roller for correctively varying the speed of said motor for preserving said desired tension in the moving web, said means for supplying constant fluid pressure to said cylinders comprising a reservoir having a large capacity compared with said cylinders and being constantly connected by conduit means to said cylinders, the relative capacity of said reservoir and cylinders being such that normal operational movement of the pistons produces only insignificant change in pressure within the reservoir.

7. In the apparatus defined in claim 6, said motor speed varying means, being operatively connected between the loop roller and said Web drive motor.

8. In the apparatus defined in claim 6, said cylinder and piston assemblies constituting the sole support for said loop roller.

References Cited UNITED STATES PATENTS 1,626,409 4/1927 Gwinn 226 X 2,544,467 3/1951 Michel 226-44 X 3,229,881 1/1966 Eckhardt 226-195 M. HENSON WOOD, 111., Primary Examiner.

R. A. SCHACHER, Assistant Examiner. 

1. A WEB TENSIONING APPARATUS COMPRISING A PAIR OF WEB FEED ROLLERS, AN ELECTRIC MOTOR DRIVING SAID ROLLERS, A PAIR OF PARALLEL IDLE ROLLERS HAVING FIXED AXES, A ROTATABLE LOOP ROLLER MOUNTED ON A SHAFT FOR VERTICAL MOVEMENT BETWEEN AND PARALLEL TO SAID IDLE ROLLERS, A PAIR OF PISTON AND CYLINDER UNITS SUPPORTING OPPOSITE ENDS OF SAID SHAFT, A LARGE CAPACITY RESERVOIR CONNECTED TO SUPPLY CONSTANT FLUID PRESSURE TO BOTH OF SAID CYLINDERS, THE RELATIVE CAPACITIES OF SAID RESERVOIR AND SAID CYLINDER UNITS BEING SUCH THAT CHANGES IN POSITION OF THE LOOP ROLLER WITH CHANGES IN SIZE OF THE LOOP DURING CHANGES IN RATE OF FEED OF SAID WEB DO NOT SIGNIFICANTLY CHANGE SAID FLUID PRESSURE, AN ADJUSTABLE PRESSURE REGULATING VALVE FOR MAINTAINING A DESIRED FLUID PRESSURE IN SAID RESERVOIR, AN ANGULARLY DISPLACEABLE ELEMENT OPERABLY CONNECTED TO BE RESPONSIVE TO THE VERTICAL MOVEMENT OF SAID SHAFT CAUSED BY A VARIATION IN SIZE OF SAID LOOP DUE TO VARIATION IN THE RATE OF FEED OF SAID WEB, AN ERROR SIGNAL GENERATOR DRIVEN BY SAID ELEMENT IN PROPORTION TO SAID SHAFT MOVEMENT, AND A SERVO SYSTEM UNDER THE CONTROL OF SAID GENERATOR FOR COMPENSATIVELY VARYING THE SPEED OF DRIVE BETWEEN SAID MOTOR AND FEED ROLLERS TO MAINTAIN SAID DESIRED WEB TENSION. 